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Primary HDU

The Calibration FITS keywords for the primary HDU conforms to the definition for common FITS headers with caveats pertaining to the keywords DATE-OBS, OBJECT, OBSID, and SCAN. The caveats reflect the fact that the FITS file is not the result of an actual observation, but rather a bench test. Therefore, DATE-OBS's value is the day but not the time of the most recent test, OBJECT's value is ``NOISE DIODE,'' OBSID's value is ``calibration,'' and SCAN is 0.

In addition to the standard primary HDU keywords, the following additional keywords will be present:

RECEIVER
The name of the receiver whose calibration values are in the tables.
MIN_FREQ
The minimum operating frequency of the receiver and associated feedhorn for this set of calibrations.
MAX_FREQ
The maximum operating frequency of the receiver and associated feedhorn for this set of calibrations.
NBEAM
The number of spatially separate RF signals the receiver is able to accept.
TAUZENIT
The opacity per unit air mass (for some receivers, this may simply be a sensible default to be used until a skydip has been performed).
ETAL
The rear spillover and scattering efficiency.
APEREFF
The aperture efficiency.
BEAMEFF
The main beam efficiency.
XANGLE1
The linear polarization angle (optional depending on recievers database).
XANGLE2
The linear polarization angle (optional depending on recievers database).
YANGLE1
The linear polarization angle (optional depending on recievers database).
YANGLE2
The linear polarization angle (optional depending on recievers database).

In version 2.2, all of the above quantities are assumed to be independent of receptor, azimuth, elevation or frequency within a given receiver's passband.


next up previous
Next: Receiver Calibration Binary Table Up: gbtMeasFits Previous: Background
Bob Garwood
2011-07-25